Set missing attribute self.server in _create_and_attach utility

Modifies _create_and_attach utility method so that it sets self.server
attribute. The test, test_attach_detach_volume was failing because it
expected the attribute to be set but it was not.

Fixes: bug #1214219
Change-Id: I88222cdf264e938f492058ab2d476406074aea40
Merge "Set missing attribute self.server in _create_and_attach utility"